فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri - Paris Observatory

Also known as Gemma, the brightest star in Corona Borealis (visual
magnitude 2.23). Alphekka is an A type dwarf lying at about 7
→ light-years.
Actually it has a faint Sun-like (G5 V) companion,
that produces an eclipse of the primary every 17.4 days.

A spherical volume of hot plasma over a broader → accretion disk
around a → black hole.
The observation of energetic X-ray emission from black holes, which is inconsistent with
→ thermal emission from an accretion disk,
is attributed to the presence of a putative hot corona.
It has been widely postulated that the → hard X-rays
are the product of
→ inverse Compton
scattering of seed photons from accretion disks by hot ccoronae
(See, e.g., F.L. Vieyro et al., 2010, arXiv:1005.5398 and R. C. Reis & J. M. Miller,
2013, arXiv:1304.4947).

1) The outermost atmosphere of the Sun immediately above the
→ chromosphere, which can be seen during a total Solar eclipse.
It consists of hot (1-2 × 106 K), extremely tenuous gas (about 10-16
g cm-3) extending for millions of kilometer from the Sun's surface.
2) Meteorology: A set of one or more colored rings of small radii,
concentrically surrounding the disk of the Sun, Moon, or other
luminary when veiled by a thin cloud.

The Northern Crown. A small but prominent northern
→ constellation that lies east of
→ Arcturus, between → Boötes
and → Hercules, and comprises a distinctive arc formed by
the stars seven stars. Abbreviation: CrB; genitive: Coronae Borealis.

An instrument which, when used in a telescope,
produces an artificial eclipse, permitting the study of the
→ solar corona without a total eclipse of the Sun.
It was invented in 1930 by the French astronomer Bernard Lyot (1897-1952).

A technique used to observe a relatively dim object (like an
→ exoplanet) lying close to an
outshining bright source (such as star). This is done by blocking the
bright object, in the same way the → solar corona
is observed using a → coronagraph.

A part of the → solar corona where the gas density and the
temperature are
higher than in its vicinity. The coronal condensations are visible on
the solar limb, above → sunspot groups. Images in X-rays and
those supplied by → coronagraphs in white light
reveal that such condensations consist of structures in the form of nodes,
underlining the corona magnetic field (M.S.: SDE).

A component of the → interstellar medium in the Galaxy
which appears as pockets of gas at temperatures of over one million degrees,
but extremely low densities of 104 atoms per cubic
centimeter. The hot coronal gas is believed to be material
blown out of violent supernova explosions. It is called "coronal gas",
after a similarity with the hot gas in → solar corona.

An area in the → solar corona
which appears dark in X-rays and ultraviolet light. The gas density in these
areas are very low, about 100 times less than that of coronal
→ active regions.
The magnetic field lines in a coronal hole extend out into
→ interplanetary space
rather than returning to the Sun's surface, as they do in other parts of the Sun
(→ open magnetic field line).
Ionized hot gas can escape easily along such a path, and this brings about
high speed → solar wind streams.

An → emission line in the spectrum of the
→ solar corona caused by highly ionized
metal ions; especially those of iron, such as the red and
green lines at 6375 Å and 5303 Å [Fe X] (Fe9+ ion)
and [Fe XIV] (Fe13+ ion), respectively. From their discovery in
1870 until 1939, it was believed
that these → forbidden lines would be due
to an unknown element, called → coronium.
Ultraviolet and X-ray coronal lines are also
detectable in stars.

An arc-like structure in the Sun's → corona
that is found around → sunspots and in
→ active regions.
These structures are associated with the closed magnetic field lines that
connect magnetic regions on the solar surface.
The loops are sometimes as high as 10,000 km with their two ends situated in
photosphere regions of opposite magnetic polarity. This implies that the coronal loops
are tubes of magnetic flux filled with hot plasma.
They last for days or weeks but most change quite rapidly.

A huge eruption of material from regions of the solar corona in which the
magnetic field is closed, but which suffer an extremely energetic
disruption. Over the course of several hours up to 10,000 billion kg
of this material is ejected into
→ interplanetary space with a a speed of as high as 3000 km/s.
CMEs are most spectacularly observed by a white light coronagraph located outside
Earth's atmosphere. Such observations from Skylab in the early
1970's were the first to reveal this phenomenon.
CME's disrupt the flow of the → solar wind
and can produce intense
electromagnetic disturbances that can severely damage satellites and
disrupt power grids on Earth. When these ejections reach the Earth, they give rise to
→ geomagnetic storms.
The frequency varies with the → solar cycle;
during solar minimum they come at a rate of about one per week,
and during maximum there is an average of about two or three per day. See also
→ interplanetary coronal mass ejections (ICME).

A bright, narrow stream of particles traveling through the Sun's corona,
visible in images taken with a coronagraph or during a total solar
eclipse. Coronal streamers represent the most outwardly extended
structures in the solar corona and result from the interaction between
the solar slow wind and the large-scale magnetic field.
→ helmet streamer.

A part of the → solar corona defined by the
→ emission lines of hot gases. These emission lines include
the so-called → forbidden lines of
the strongly ionized atoms of iron, calcium, and other elements. The E
corona is thinner than the → K corona and the
→ F corona (M.S.: SDE).